At least as early as the 1950's, there has been an important need for cables having low noise qualities where the noise in the cable is induced by mechanical movement of the cable (as used herein noise refers to an extraneous electrical signal in a cable and mechanical noise refers to noise caused by mechanical movement of the cable, e.g. movement of the conductor and/or shield with respect to the dielectric). In the early 1950's shock and vibration measurements of missile firings were attempted. Cables were attached to the measuring equipment and a strategically placed accelerometer. The measurements were difficult to make because noise generated in the cable by vibration of the cable and the accelerometer often masked the signal to be measured.
More recently the medical industry has developed equipment requiring low mechanical noise cables. For instance, when a patient is hooked to an EEG machine the attaching cables vibrate as the patient runs on a threadmill. Other medical applications for low mechanical noise cables include EKG machines where cables are attached to the patient's head. In addition, high beam amplifies, oscilliscope probes and the like require low mechanical noise cables.
Representative of the attempt to provide the needed cables is U.S. Pat. No. 2,622,152 to S. G. Rosch which suggests a coaxial cable having a central metallic conductor surrounded by a dielectric material wrapped with dielectric tape formed of a conductive material and surrounded further by a shielding layer which is in turn surrounded by an insulating jacket. Similarly, U.S. Pat. No. 2,614,172 issued to Greenfield et al., suggests enclosing a thermo magnetic core within a layer of metal surrounded by a tube of dielectric material, the tube in turn surrounded by a metallic shielding material comprising a braid of fine wires of good electrical conductivity.
Further disclosures such as U.S. Pat. No. 3,209,064 issued to Cutler, suggests a plurality of pairs of conductors mutually insulated and surrounded by insulating members of polyethylene material in a separate layer of polyethylene-type insulating material. Surrounding the separate polyethylene material is a conductive shielding member and insulating jacket similar to those previously discussed.
The most recently discovered attempt to fulfill the need for low mechanical noise coaxial cable is Gulton Instrumentation Division's (of E. I. duPont de Nemours & Company) C-5 series cable which includes a Teflon* layer as the primary insulator over a copper-weld conductor and bonding the two together to prevent relative movement therebetween. FNT *Federally Registered Trademark of E. I. duPont de Nemours & Company
None of the devices discussed above suggests or in any way teaches applicant's invention of a low mechanical noise cable having a central conductor surrounded by a dielectric in turn surrounded by electrical shielding embedded in a conductive material and said elements preferably held in place by jacketing means.